488 E. ELEANOR CAROTHERS 



From my cytological studies, I do not hesitate to say that 

 form B is a Trimerotropis, and furthermore, it is a question if 

 Circotettix suffusus and Trimerotropis fallax, as they are now 

 recognized, do not even constitute a single species. 



4. Correlation of chromosomal behavior and Mendelian principles 



The evidence pointing to the chromosomes as the bearers of 

 the heredity determiners has been summarized so often recently 

 that I shall not repeat the process. One of the chief difficulties 

 that cytological research has met with has been the impossi- 

 bility of distinguishing between the chromosomes derived from 

 the two parents. While it has been clear that homologous 

 chromosomes segregate into different gametes, it has been 

 impossible to say, except in the cases of the tetrads composed 

 of unequal dyads recently reported (Carothers '13, Wenrich '14, 

 Robertson '15), that all of the chromosomes brought in by the 

 egg do not pass into the female-producing spermatozoon, as 

 was suggested by Payne ('09) as a result of his study of Gryl- 

 lotalpa borealis. 



Attempts have been made to determine the behavior of the 

 paternal and maternal chromosomes in the maturation divisions 

 and also to correlate given chromosomes with given somatic 

 characters. Heretofore, the most promising line of attack 

 on such problems has been through hybridization of forms with 

 morphologically different chromosomes. The most noted of 

 these experiments is that of Moenjdiaus ('05). He crossed 

 Fundulus heteroclitus and Menidia notata. The former has 

 long, straight chromosomes, while those of the latter are short 

 and curved. In the first few cleavages of the hybrid zygote, 

 the chromosomes derived from one parent remained separate 

 from those derived from the other. In later divisions the 

 chromosomes became mixed on the spindle. But the important 

 fact was demonstrated that the chromosomes derived from each 

 parent maintained their morphological identity. The embryos 

 did not develop beyond the closing of the blastopore. 



Perhaps the most significant recent work along the line of 

 hybridization is that of Federly ('13) who has combined breeding 



